The New York Time health blog has a piece about a debate between two British scientists, where one is heavily critical of the practice of circumcision on infant males.
The article acknowledges that numerous studies have shown medical benefits to male circumcision, including reduced female to male H.I.V. transmission, reduced likelihood of carrying the human pap virus (which is harmless to men but can be transmitted to women and lead to cervical cancer), and a smaller chance of getting over sexually transmitted infections.
In light of the evidence that male circumcision decreases penal infections, which could have decreased fertility, it makes sense that ancient cultures took it upon themselves to circumcise all men as a precaution. This is in line with modern childhood vaccines - no one asks a child whether he or she would like to risk getting a terrible disease - the common wisdom is to do the prophylactic on everyone.
Furthermore, a Jewish bris (the Hebrew word for the covenant between Abraham and G-d, which included Abraham and all of his male decendent's circumcision) is a wonderful public ceremony welcoming a new boy into his community. Many religions have such a ceremony, and it is one of the most joyous.
However, the question remains that even if male circumcision is a medically sound idea, and if welcoming a new boy into his religious community is a wonderful ceremony, why must they be together? Why can't the circumcision be in private, and then the naming ceremony and party be in public? Why would a religion that in some sects is so Victorian about sexuality and modesty performs surgery on a boy's penis in public?
Perhaps in ancient times, the community needed to be sure that all of the men were circumcised. Otherwise, the first to find out might be the man's intimate partner, who might not be in a position to protest have intercourse with an uncircumcised man, despite her desire not to put herself at higher risk.
In this light, male circumcision becomes a conscious public health decision, done publicly to ensure compliance, and done on infants to avoid compromising the modesty of an older boy.